6 Americans, 1 Briton vanish at sea while sailing from New Zealand to Australia

"Nina," a historic schooner built in 1928, was last seen in the South Pacific off the north coast of New Zealand three weeks ago.

By Henry Austin, NBC News contributor

Six Americans and a Briton have been missing at sea for more than three weeks after setting sail from New Zealand, officials said Thursday.

The seven were aiming to sail the 70-foot schooner Nina to Newcastle, Australia.

The New Zealand Herald on Friday identified four of the people on the boat: David Dyche, 58; his wife, Rosemary, 60; their son David, 17; and Evi Nemreth, 73, of Boulder, Colo., a maritime technology expert and retired University of Colorado professor.

A 35-year-old British man, a 28-year-old American man and an 18-year-old American woman on board have not yet been identified.

A statement from Maritime New Zealand released early Thursday expressed "grave concerns" for the Nina's crew.

Maritime New Zealand via AP

The Nina was built in 1928.

The vessel left the Bay of Islands area of northern New Zealand on May 29. It has not been heard from since June 4, when the ship was 370 miles west-north west of Cape Reinga in "very rough" conditions with winds gusting to 68 mph and 26-foot swells.

Authorities said the vessel's emergency beacon has not been activated.

Rescue Coordination Centre New Zealand search and rescue mission coordinator Kevin Banaghan said that a military aircraft had covered a 160,000 square nautical mile search area on Tuesday, with an additional 324,000 square nautical miles examined on Wednesday.

"No sign of the vessel has been found," Banaghan said. "We do hold grave concerns for the Nina and her crew but remain hopeful of a positive outcome."

On Thursday, the rescue center was set to search the northern shores of New Zealand, in case the crew had abandoned ship and attempted to raft to safety — but “windy and rainy” weather conditions delayed the effort, said spokesman Steve Rendle.

The huge search was launched after family and friends raised concerns about the crew's whereabouts.

The Nina was built in 1928. It is also equipped with a satellite phone and a spot beacon, which allows tracking signals to be sent manually.